Sitting discomfort can be caused by a variety of different conditions. One common condition that is at least a contributory cause if not a primary cause to sitting discomfort is the existence of excessive pressure on portions of the user's body while in a seated posture resting upon a seat or other underlying sitting support structure.
The pressure associated with a user sitting upon a seat has two basic components including the force component and the area component. The greater the force the greater the pressure will be. The lesser the area over which the force is applied, the greater the pressure will be. The force component of this pressure is typically primarily caused by the force of gravity acting on the mass of the user tending to pull the user down toward the Earth. This force is resisted by the seat or other underlying sitting support structure with resultant pressure being felt by the user through nerves in the user's body proportional to this force.
As the force of gravity is substantially constant on the Earth, the primary factor in calculating this gravity force is the mass of the user. While in a seated position it is primarily the mass of the torso, head and arms of a user, as well as to some extent the mass of the hips and upper legs of the user, which are the portion of the mass of the user which contribute to the force component of pressure experienced by the user. Because users often have little control over their body mass, it is typically difficult or impractical to minimize pressure associated with sitting by reducing the force being exerted by gravity on the user and resisted by the underlying sitting support structure.
The area over which this force acts is the second parameter that establishes the pressure felt by the user. In particular, as the area over which this force acts is increased, the pressure experienced is decreased. Pressure is typically not uniform within the area that the force applies. Furthermore, the overall dimensions of the user restrict to some extent the maximum amount of area available for distribution of this force. Typical seat cushions provide some degree of padding so that the forces are distributed somewhat over a larger area rather than being concentrated at small areas or points beneath the user. However, cushions generally only act to a relatively small extent in distributing these forces. In particular, as a solid structure, cushions exhibit a limited amount of movement and thus only modify associated pressures partially.
It is known in the prior art to utilize air filled cushions as a sitting aide in certain circumstances. For instance, hemorrhoid donuts are known in the prior art which are partially inflated and then the user sits upon such a structure. With such air filled cushions, generally upper and lower layers of substantially air tight material are provided surrounding an interior space. The air cushion is filled sufficiently so that the upper and lower layers do not come into contact with each other. The air filled cushion automatically alters it geometry to conform to that of the user typically to a greater extent than soft material cushions. Thus, a higher degree of force distribution over the area involved is achieved.
Prior art air filled cushions have not been entirely satisfactory for a variety of reasons. First, the geometry of a user when seated in an upright manner is not a simple geometry. Thus, merely providing a cushion beneath the underside of the user is often insufficient to effectively distribute forces sufficient to avoid pain for the user. This is particularly true when the user experiences lower back pain and pain about the hips of the user.
Secondarily, air cushions have a tendency to provide too much movement between the user and the underlying sitting support structure. It is generally desirable when a user is utilizing a sitting support structure that the user be able to remain substantially still when seated. If the user must “balance” upon the cushion in a manner similar to balancing upon an air filled large ball, the user will be subconsciously tensioning and relaxing a variety of different muscles to maintain a desired posture. While such “exercise” may be beneficial for short durations, over a long period of sitting, such muscle activity soon leads to muscle fatigue and enhanced discomfort for the user.
When the underlying sitting support structure is a seat of an automobile, additional forces are being applied on the user associated with bumps in the road and acceleration around corners or in a forward or backward direction during acceleration and braking. Prior art air filled seat cushions have either failed to provide an adequate degree of immobility to keep the user comfortably seated in a single position, or have provided too little cushioning support so that concentrations of force occur within the area over which the pressure is experienced, so that pressure points still exist at which excessive forces lead to pain and other discomfort for the user. Accordingly, a need exists for an improved lumbar and back support cushion which can not only support upper legs of the user but also the lower back and upper back of the user in a manner both effective to provide a comfortable and secure body position for the user but also minimize force concentrations.